might be a useful way to communicate with other survivors without compromising you safe location.potential problem, bandits or other bad type people camping at the board to see where you come from, or just to kill you and take your stuff.

It would be pretty useful. Think of the stuff that was posted on the walls in left 4 dead. That information could be vital to someone who is following in your foot steps. Ie "Riverside overrun". I dont know how long power would last so written messages might be the only communication non military personnel have.